Model Test Of Bending Failure Mode And Bearing Capacity Of CFG Pile Considering Eccentric Effect

With the development of transportation,the mileage of railway and highway in China increases year by year.The safety of vehicles in the process of driving needs to be paid attention to.Therefore,the requirements for the bearing capacity and stability of subgrade are also improved.Composite foundation treatment technology,as one of common foundation treatment methods,has been widely used in railway construction.Artificial foundation with piles as vertical reinforcement and bearing the upper load together with soil around piles is commonly used in composite foundation.As a result,how to calculate and design the bearing capacity of single pile properly begins to play an important role in the design of composite foundation.In practical engineering,due to improper construction or horizontal lateral displacement of pile top during operation,the inclination of pile will increase and the bending moment of pile top will appear,which may reduce the ultimate bearing capacity of pile.Therefore,in this paper,the bearing capacity of CFG pile is studied by indoor model test.The main work and conclusions are as follows:(1)Based on the influence of the vertical degree of pile,the eccentricity of pile top load and the strength of soil around pile on the ultimate bearing capacity of single pile,an laboratory model test was carried out.A set of loading device was designed independently,and the pile was loaded by the method of slow maintaining load.The loading termination condition was the failure of the pile.The load and settlement curves were recorded and drawn during the loading process.(2)After the failure of each group of test piles,the foundation soil shall be excavated and the failure mode of piles shall be observed.For vertical piles under vertical axial load and piles with an inclination of 5%,there are three bending points during failure.For the pile with inclination of 10% and subjected to eccentric load,there are two bending points during failure,and the failure form is in an inverse "s" shape.One bending point is located near the position where the pile cap contacts the pile,and the ultimate bearing capacity of the pile decreases with the increase of load eccentricity at the top of the pile;For the pile under the coupling action of pile body inclination and pile top eccentric load,there are also two bending points during failure,and the failure form is "s" shape.When the strength of local foundation soil is high,the failure form is similar to that of the pile only affected by inclination.(3)When the inclination of pile body is less than 10%,it has little effect on the ultimate bearing capacity;The ultimate bearing capacity of pile decreases with the increase of pile top load eccentricity and increases with the increase of foundation soil strength.(4)Through orthogonal test and multiple regression analysis,the significance and order of the influence of three factors on the bearing capacity are obtained: foundation soil strength > pile top load eccentricity > pile inclination.The regression equation between ultimate bearing capacity and pile inclination,pile top load eccentricity and foundation soil strength is established.The goodness of fit of the equation reaches 0.927.The equation is used to predict the remaining test groups.The average relative error between the predicted value and the test value is 9.02%.